In one known apparatus for controlling the warp beam of a warp knitting machine, German Patent DEOS 3832695 discloses a pressure roll engages the warp beam and drives a tachogenerator which produces electrical signals representing the actual yarn delivery speed, and thus a value of the amount of yarn delivered. In this apparatus, a controller, such as a conventional microprocessor, compares the generated signals with a predetermined knitting machine operating standard derived from the yarn consumption per knitting loop, a stored pattern program, and the desired yarn consumption for each knitting course.
A control signal is generated to the drive mechanism of the warp knitting machine for controlling the speed of the warp drive mechanism. In one embodiment of this known apparatus, the drive mechanism is interposed in a control loop which allows a comparison of the control signal with the actual speed of the drive mechanism as measured by a second signal generator operatively connected to the warp beam drive motor. A signal generator operatively connected to the support arm generates a pivot signal representative of the angulation of the support arm toward the warp beam to determine the diameter of the yarns wound on the warp beam. Based upon this measured diameter, the warp beam drive mechanism is set accordingly.
Operational problems arise in this warp knitting machine control system because the control system tends to oscillate as a result of the decreasing diameter of the warp beam. Because the moment of inertia of a warp beam changes considerably as its diameter decreases, i.e., with the fourth power of the radius of the warp beam, the control signal and in the control loop tend to oscillate, especially when the warp beam diameter is small. A small diameter warp beam must be accelerated or decelerated quickly to compensate for the quickly varying yarn feed requirements which vary from course to course.
When the generated signals are electronically damped, the warp beam drive mechanism responds to the control signals much more slowly. This problem becomes more apparent when the drive of the warp beam is controlled individually with respect to the yarn withdrawal speed for each course of stitch loops within a repeat to satisfy the yarn delivery requirements, which differ from one course to another.
In accordance with the present invention, it has been discovered necessary to amplify the control signal when the warp beam diameter is small to gain increasing control over the warp beam. The amplification should not occur, however, when the warp beam has a relatively large diameter produced by the full yarns wound on the warp beam. A greatly amplified control signal would lead to a relatively intensive control and overshooting of the desired change in the warp beam yarn withdrawal rate so that the large diameter warp beam would accelerate or decelerate faster than desired. In view of the greater inertia of the larger diameter warp beam, the result is a corresponding longer decay time. For this reason, the amplification for larger diameter warp beams must be reduced to prevent the overreaction in the warp beam control.